Minae Mure

Biomimetic oxidation of alcohols by coenzyme PQQ-trimethyl ester

Abstract Oxidation of alcohols to corresponding carbonyl compounds by coenzyme PQQ-trimethyl ester was performed in the presence of aluminum t-butoxide or aluminum chloride under anaerobic conditions. Reduced PQQTME (PQQTMEH 2 ) was obtained by acidification of an aluminum complex of reduced PQQTME which was isolated in the reaction.

Novel addition of nitroalkanes to o-quinones

Abstract A novel addition reaction of nitroalkanes to o-quinones is found to give 1,3-dioxole derivatives.

Preparation and characterization of iminoquinone and aminophenol derivatives of coenzyme PQQ

Abstract 5-Iminoquinone derivative of PQQ was easily prepared by treatment with ammonia. Reduction of the iminoquinone with methylhydrazine gave aminophenol derivative of reduced PQQ. Spectral characteristics of them are presented.

Reaction of coenzyme PQQ with amino acids. Oxidative decarboxylation, oxidative dealdolation (Cα–Cβ fission) and oxazolopyrroloquinoline (OPQ) formation

The reactions of coenzyme PQQ (pyrroloquinolinequinone) and several amino acids have been investigated in vitro. PQQ catalyses the oxidative decarboxylation of α-amino acids to afford the corresponding aldehydes under aerobic conditions. During the catalytic cycles, PQQ is gradually converted into oxazolopyrroloquinoline (OPQ) derivatives to be deactivated. Product analyses indicate that the reaction proceeds via an ionic mechanism that involves a carbinolamine-type adduct as a key intermediate. From this intermediate, direct decarboxylation (major path) and dehydration followed by decarboxylation and hydrolysis or by intramolecular cyclization (minor paths) competitively occur to give the quinol, the aminophenol and the OPQ derivative, respectively. In the reactions with β-hydroxy amino acids, tyrosine and tryptophan, oxidative dealdolation (Cα–Cβ fission) proceeds effectively. The similar ionic mechanism that involves the carbinolamine-type intermediate is suggested by the product analyses under both aerobic and anaerobic conditions.

Oxidative Cα–Cβ fission (dealdolation) of β-hydroxy amino acids by coenzyme PQQ

Coenzyme PQQ is demonstrated to catalyse the oxidative Cα–Cβ fission (dealdolation) of β-hydroxy amino acids under very mild conditions.

The reaction of coenzyme PQQ with hydrazines

The reaction of coenzyme PQQ with hydrazines, which are known to be inhibitors of quinoprotein amine oxidases, has been investigated in vitro. Only the redox reaction is observed in the reaction with phenylhydrazine, methylhydrazine,N,N-dimethylhydrazine, and N, N′-dimethylhydrazine. However, the PQQ adduct formation occurs concomitantly in the reaction with 4-nitrophenylhydrazine, and only hydrazone formation is observed in the reaction with 2,4-dinitrophenylhydrazine [(3) and (4), respectively]. Kinetic studies reveal that the order of the redox reactivity is phenylhydrazine ≃ methylhydrazine > N, N′-dimethylhydrazine N,N-dimethylhydrazine, which does not correlate with the two-electron redox potentials of these hydrazines. The reactivity of the PQQ model compounds [PQQ, PQQTME, and (5)–(10)] in the oxidation of methylhydrazine is also examined, the relative reactivity seems to be related to the reactivity of the quinone functional group toward nucleophilic addition (hydration), but does not reflect the two-electron redox potentials. These results suggest that reduction of PQQ with hydrazines proceeds via covalent addition of hydrazines to the quinone to form a carbinolamine type intermediate followed by electron flow from the nitrogen of hydrazines into the quinone moiety.

Oxidation of D-glucose by coenzyme PQQ: 1,2-enediolates as substrates for PQQ oxidation

Studies on the oxidation of D-glucose and related substrates with coenzyme PQQ have established that 1,2-enediolates are efficient substrates for PQQ oxidation.

Chemical Behavior of Coenzyme PQQ toward Amine Homologs

Nonenzymatic oxidation of several amine homologs was carried out under mild conditions. Aliphatic amines were efficiently oxidized by PQQ in CTAB micellar system. In the case of ω, ω’-diamines, length of the carbon chain was significant; the reaction rate became larger with the increase in the carbon number. On the contrary ethylenediamine showed competitive inhibition forming the cyclic adduct, a fused diazine. Carbonyl reagents such as hydrazines and aminoguanidine were also oxidized by PQQ, but the latter compound deactivated PQQ by forming the 1,2,4-triazine derivative under catalytic conditions or at lower pH region.